Buffett noted in the letter that BNSF railroad, the massive
transport company Berkshire owns, "dramatically improved" its
service after a poor performance in 2014 he had apologized for.
Berkshire spent about $5.8 billion in capital expenditure to
improve service.

Together with BNSF, the so-called "Powerhouse Five", which
includes Berkshire's five most profitable non-insurance
businesses, earned $13.1 billion last year.

Berkshire bought more shares in each of its "big four"
investments last year: American Express, Wells Fargo, Coca-Cola,
and IBM.

In 2015, Berkshire's subsidiaries contracted for 29 so-called
bolt-ons, which are other businesses that are seen as great fits
for the existing subsidiaries. These came at a cost ranging
from $300,000 to $143 million.

The letter contained a preview of the forthcoming annual meeting.
As earlier reported, there will be a
livestream of the Q&A portion of the meeting between
Buffett, vice chairman Charlie Munger, journalists and investors
for the first time, hosted by Yahoo Finance.